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Despite growing concern over toxic ingredients in e-cigarettes, many parents think the vapor is safe for children and use the products around their kids, new research has found.

Only one in five parents who use e-cigarettes have strict rules against vaping in their homes and cars, according to the study published Monday in Pediatrics. Parents who vape and smoke are more likely to enforce a smoke-free than a vape-free policy at home.

The report shows the need for a warning label to caution that wherever people would never smoke a cigarette, they should also never vape, said Dr. Jonathan Winickoff, the lead author, a pediatrics professor at Harvard Medical School and MassGeneral Hospital for Children, and director of pediatric research at the Tobacco Research and Treatment Center at Massachusetts General Hospital.

“The study findings are frightening,” Winickoff told TODAY. “Parents are doing this to their children without understanding what the effects are and what the science shows already for these products.

“With electronic cigarettes, we don’t know where this story ends, but what we see so far is very concerning.”

Many people think e-cigarettes emit just water vapor. But there’s no water in these products at all; rather, it’s a “sticky goo” that gets turned into ultra-fine aerosol with tiny particles that get inhaled deep into the lungs, Winickoff said.

The aerosol contains very high concentrations of nicotine, which is not safe for a child’s developing brain; tobacco-specific nitrosamines, which are some of the most carcinogenic substances known; and heavy metals that leak from e-cigarette heating coils, he added.

When people vape around children, the kids can get nicotine into their systems in three ways:

by inhaling the aerosol that parents vape.

by ingesting the nicotine and other toxic compounds that are left on surfaces. That sticky goo, once aerosolized, coats floors, bedrooms, kitchens and other places in the home in a nicotine-laden layer, Winickoff said. Kids are “like little human mops” — especially children who are crawling around — because they touch everything and put their hands in their mouth all the time.

by absorbing it directly through their skin: Kids’ skin is thinner, so just like an adult who is trying to quit smoking might put a nicotine patch on his or her skin, a child whose parents vape can absorb the substance that way.

“We think parents are trying to use these products to protect their kids. Unfortunately, what we’re seeing is they’re using these products in ways that they would never dream of using a cigarette: right in front of their kids, in their home, in their car and that’s disturbing,” Winickoff said.

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The study was based on responses from 943 parents in Indiana, North Carolina, Ohio, Tennessee and Virginia, who were current or former smokers.

The findings come days after another study found 7 percent of women used e-cigarettes around the time of their pregnancy, with almost half doing so because they thought the products were less harmful than regular cigarettes. The survey included 3,277 women in Oklahoma and Texas who recently gave birth.

Electronic vapor products are not safe to use during pregnancy because most contain nicotine, a "developmental toxicant," the report from the Centers for Disease Control and Prevention warned.

The biggest risks include stillbirth, pre-term delivery and placental abruption, a condition where the placenta separates from the uterus before birth, said Dr. Lindsay Breedlove Tate, an OB/GYN at Baylor Scott & White All Saints Medical Center in Fort Worth, Texas.

“It’s scary to know these things can happen and that it’s something that can be prevented,” she noted. “There’s not the added smoke inhalation that you get with traditional smoking, which leads to a common misperception that e-cigarettes are completely safe in pregnancy.”

Parents are more likely to protect younger children from their vaping, the Pediatrics study noted, but e-cigarettes are dangerous for kids of all ages, from infants to adolescents, Winickoff warned.

Besides exposing developing brains and lungs to high concentrations of nicotine — which affects lung growth and normal weight gain — the very act of seeing parents vaping boosts the chances their kids will go on to use e-cigarettes, too.

The brains of teens exposed to nicotine at home may also be primed to respond more dramatically when they vape or inhale a tobacco product themselves, so they’re more likely to get addicted, Winickoff noted.

He urged parents to quit all tobacco products, but if they couldn’t stop using them to at least make their home and car completely vape- and smoke-free.

NBC's Tonya Bauer contributed to this report.

A. Pawlowski

A. Pawlowski is a TODAY contributing editor focusing on health news and features. Previously, she was a writer, producer and editor at CNN.